The identity and amount analytes, including but not limited to nucleic acids, proteins, and cells, can provide valuable information about the samples and subjects from which they are taken. For example, the presence or severity of an infection can be measured. Markers for a wide range of conditions, from HIV to traumatic brain injury, can be assessed and quantified. In particular, portable methods for measuring and characterizing analytes are useful. Devices capable of analyzing samples can permit use of diagnostics and assays in remote locations, in resource-poor settings, or at the point of care.